We present a 71-year-old woman with spontaneous perinephric hematoma due to a rupture of pseudoaneurysm of the right renal artery on the fourth day after radical cystectomy and bilateral ureterocutaneostomy for bladder cancer. This patient received steroid therapy for chronic rheumatoid arthritis for several years. The digital subtraction angiography of the right renal artery showed two pseudoaneurysms in the anterior inferior segmental branch and the posterior inferior segmental branch. Transarterial coil embolization of the right renal artery proximally and distally to the two aneurysms was performed without complications. Moreover, the additional angiography showed typical string-of-beads appearance and small aneurysms in abdominal visceral arteries, suggesting segmental arterial mediolysis (SAM) as a possible etiology. Differential diagnoses of SAM are discussed.